Japanese Utility Model Publication No. 50-13443 (Japanese Utility Model Reg. No. 1,110,594) shows that the exposed area of a photosensitive material is indicated by measuring the horizontal distance between the position of the recording head which advances in the horizontal direction as scanning proceeds and the recording start point or the end point. The apparatus disclosed in the publication enables to measure the exposed area only in the horizontal direction, hence the remaining non-exposed area, on a sheet of photosensitive materials.
Japanese Patent Publication No. 52-18601 shows that image frames for respective color separation images are vertically allocated on a sheet of photosensitive materials, and that the color separation, e.g., for Yellow, Magenta, Cyan and Black is made so as to record respective separation images with coinciding with the image frames. Also, in this method the horizontal position of a recording head relative to a photosensitive material is detected and the exposed area, hence the remaining non-exposed area, of the sheet is measured only in the horizontal direction.
It will be advantageous for promoting the operating efficiency of electro-optical scanning apparatus that color separation images are arranged on a comparatively large sized sheet of photosensitive materials so as to utilize the whole area in which reproduction images are fully allocated not only in the horizontal direction, but also in the vertical direction and or in the matrix.
In view of the above prior arts, none of them is suitable for promoting the operating efficiency of scanning apparatus, and it is impossible with the prior art structures to measure the exposed area, hence the remaining non-exposed area, of the whole range of the photosensitive material. In order to record reproduction images on a photosensitive material in such a manner as above, the recording point must be detected in the horizontal direction (hereinafter defined as the subscanning direction) as well as in the vertical direction (hereinafter defined as the main scanning direction). In prior arts as mentioned above, it is impossible to measure the exposed area in the main scanning direction and moreover there is the disadvantageous possibility that adjacent images overlap.